Semiconductor packages equipped with wireless data and communication systems incorporate various RF (radio frequency) transmitting structures, which sometimes are built on-chip. RF signals are generally considered to have a frequency falling in approximately the 3 kHz to 300 GHz range, with frequencies in the domain between about 300 MHz (0.3 GHz) and 300 GHz typically being referred to as microwaves. Electromagnetic RF waves or signals are conveyed through the semiconductor packages or devices by conductive structures referred to as “transmission lines.” Transmission lines, as an example, are used for interconnecting individual electrical elements together within an integrated circuit (IC) or MultiChip Module.
In general, a transmission line structure generally includes at least two electric conductors or lines, where one of the lines forms a ground line (also referred to as “ground plane”) and the other forms a signal line. The signal line is variously arranged and combined with one or more ground planes or ground lines to form different types of conductive transmission line structures such as microstrips, striplines, and waveguides to serve various RF signal applications. The signal lines and ground lines are generally supported and separated by some type of insulating substrate or material, such as a dielectric.
As semiconductor technology continues to advance and chip package size shrinks, the distance between metal layers in the conductive CMOS (complementary metal-oxide semiconductor) structure becomes smaller resulting in increasingly larger capacitance between the metal layers which compromises performance of RF devices.